1. Field of the Invention
This invention relates to a method of preparing a surface-mounted wiring board, and more particularly to a method of preparing a surface-mounted wiring board in which a process of coating die pads and bonding pads by Au-plating is modified.
2. Description of the Related Art
A hybrid circuit (device) formed by arranging and mounting electronic components such as SOP-LSIs (Small Outline Package Large Scale Integrated circuit), QFP-LSIs (Quad Flat Package Large Scale Integrated circuit), LSI chips, bare chips, IC (Integrated Circuit) chips, chip capacitors, and chip resistors on one face or both faces of a wiring board such as a multilayer wiring board has been widely applied to various types of electronic devices.
In such a hybrid circuit (device), each of the electronic components is arranged and mounted on a die pad section metallized at a predetermined area of the wiring board and is electrically connected as prescribed to a bonding pad section arranged around the die pad section by, e.g., wire bonding. More specifically, the die pad and bonding pad surfaces made of Cu or Ni are further provided with an Au-plated coating to stabilize them. On the die pad section thus processed, an electronic component is arranged and mounted by means of a reflow soldering process using, e.g., a cream solder. To the bonding pad section, the input/output (I/O) terminals of the electronic component, e.g., an IC chip, are electrically interconnected by a bonding wire. A hybrid circuit having predetermined electronic components arranged and mounted will thus be prepared.
By the way, a surface-mounted wiring board is generally fabricated as follows. A die pad or die pads and the corresponding bonding pads are formed, together with a circuit pattern for signal lines, at predetermined areas on one face or both faces of the wiring board by, e.g., selectively etching a copper foil layer. During this selective etching process, the conductor terminals (conductor lines for plating) for these die pads and bonding pads must be formed by drawing out to the periphery of the wiring board in preparation for Au-electroplating, which is a subsequent process. After the Au-electroplating process has been effected as prescribed with these conductor terminals as the plating terminals, a surface-mounted wiring board can be obtained.
However, the above-described method has the following shortcomings. In order to Au-electroplate these die pads and bonding pads, their conductor terminals must be drawn out to the periphery of the wiring board. This means that two kinds of line, a conductor line for plating and a signal line, must coexist on the wiring board surface, thereby decreasing the wiring density of signal line. Particularly, in cases where the number of electronic components to be arranged and mounted on the wiring board is large and the number of leads of an electronic component is large as well, numerous pads must be prepared. Consequently, the area of the conductor terminals required for Au-electroplating will naturally be increased, thereby affecting the mounting density of the wiring board.
It is therefore an object of the present invention to remove this restriction imposed on the wiring density and thereby to provide a method of preparing a surface-mounted board adapted for easily constructing a high density hybrid circuit.
It is another object of the present invention to provide a method of preparing a surface-mounted board adapted for easily constructing a highly reliable hybrid circuit.